Because of the outstanding electrical characteristics, hardness, corrosion resistance, stability and other desirable properties exhibited by palladium, it is advantageously used as a plating for electrical connectors, printed circuits, and the like, as well as for numerous other industrial and commercial applications. As a substitute for gold and platinum, palladium represents a more economical alternative, both on a simple weight basis and also in terms of covering power, due to its lower density; nevertheless it is, of course, by no means inexpensive. Consequently, alloys of palladium, and (in the particular context of the present invention) specifically with nickel, have been used in certain applications in order to further reduce costs. Baths for electrodepositing palladium/nickel alloys are taught in the art, such as in Yamamura et al U.S. Pat. Nos. 3,580,820 and 3,677,909; earlier patents disclose the use of nickel in palladium electroplating baths, not only as an alloying metal but also as a colorant, for grain size refinement, and the like, as exemplified by U.S. Pat. Nos. 1,981,715 and 2,452,308, United Kingdom patent specification No. 958,685 and Japanese Pat. No. 8769.
Despite such earlier activity, the baths of the prior art are not found to be entirely satisfactory. In some instances, they are unstable and prone to rapid decomposition and deterioration; some are too inefficient for practical use, or operate effectively only at unduly elevated temperatures; and in certain cases the nature of the deposit produced from the bath may be deficient, as being dark and/or brittle (especially in thicker sections), or as lacking brightness or specularity.
A bath intended essentially for electrodeposition of palladium, but which may contain other codepositable metals as well, as disclosed and claimed in copending application Ser. No. 183,318, filed in the name of Robert M. Skomoroski on Sept. 2, 1980 and entitled "PALLADIUM ELECTROPLATING BATH", which application is of common assignment herewith. A unique feature of the invention of that application resides in the use of 3-butyne-2-ol as a brightener, thus avoiding any need for a metallic brightening agent. Despite the benefits to be derived therefrom, and from the inventions of the aforesaid prior art patents, still a demand exists for a stable electroplating bath that is capable of efficiently producing bright, smooth, uniform and relatively stress free deposits, which operates efficiently over a wide range of current density and under convenient conditions, including mild bath temperatures.
Accordingly, it is a primary object of the present invention to provide a novel, cyanide-free bath for electrodepositing alloys of palladium and nickel, which bath is operative over a broad range of current density and at ambient to low-elevated temperatures, to produce a deposit that is relatively bright, smooth, uniform and free of stress.
It is also an object of the invention to provide a novel method for the electrodeposition of palladium/nickel alloys having the foregoing characteristics, which method can be carried out over a broad range of current density and at ambient to low-elevated temperatures.